1. Field of the Invention
The present invention relates to methods and apparatus for producing fibers and fabrics in a closed fiber spinning system, where the fibers and fabrics include a plurality of different polymer components.
2. Description of the Related Art
A number of closed fiber spinning systems are known in the art for manufacturing spunbond fabrics having certain desirable characteristics. For example, U.S. Pat. Nos. 5,460,500, 5,503,784, 5,571,537, 5,766,646, 5,800,840, 5,814,349 and 5,820,888 all describe closed systems for producing spunbond webs of fibers. The disclosures of these patents are incorporated herein by reference in their entireties. In a typical closed system, filaments are spun, quenched and drawn in a common enclosed chamber or environment, such that the air or gas stream that is utilized to quench the fibers emerging from a spinneret is also utilized to draw and attenuate the fibers downstream from the quenching stage.
In direct contrast to open fiber spinning systems (i.e., systems in which extruded filaments are not spun, quenched and drawn in a common chamber or environment and are typically exposed to the ambient environment during some or all of the fiber forming steps), closed systems eliminate any interference from uncontrolled and potentially detrimental air currents during fiber formation. In fact, a typical closed fiber spinning system limits exposure of extruded filaments to only desirable air or gas currents having selected temperatures during fiber formation, thus facilitating the production of very delicate and uniform fibers having desirable deniers that are difficult to obtain from a typical open fiber spinning system.
One important component in any fiber spinning system is the polymer delivery system, typically referred to as the spin beam, which provides molten polymer streams at a selected metering or flow rate to the fiber spinning system for extrusion into filaments by a spinneret. One type of spin beam typically utilized and highly advantageous for spinning fibers in a closed system is commonly referred to as a “coat hanger” spin beam. This type of spin beam is typically formed by two sections, constructed of metal or other suitable material, joined together in a fluid tight relationship at facing or mating surfaces, where each mating surface has grooves etched into the surface that correspond with and mirror grooves etched in the mating surface of the other section. The grooves etched on each mating surface form a profile that resembles a triangular “coat hanger” configuration.
An exploded view of a conventional “coat hanger” spin beam is illustrated in FIG. 1. Spin beam 2 includes two generally rectangular halves or sections 3 having a number of electric heaters 12 disposed within each section to heat polymer fluid flowing within the spin beam toward the spinneret. In operation, a molten polymer stream is directed (e.g., via a pump) into an inlet portion 4 of the “coat hanger” channel profile of spin beam 2 and travels into an upper portion of the triangular channel portion 6 of the “coat hanger” profile that is disposed below and in fluid communication with inlet portion 4. The “coat hanger” channel defined by the inlet portion and the triangular portion is formed by corresponding grooves disposed on the mating surfaces of the two spin beam sections 3. Upon entering channel 6, the molten polymer stream splits into the two diverging channel sections 7 of the triangular channel portion, where the split streams continue to travel and then converge within a horizontal channel section 8 disposed at a lower end of the “coat hanger” channel between the lower ends of the diverging channel sections. The horizontal channel section also extends longitudinally along a lower end of spin beam 2. Affixed at the lower end of the spin beam are a screen filter and plate 9 and a spinneret 10 having a plurality of orifices disposed along its longitudinal dimension. The screen filter, plate and spinneret also extend longitudinally along the lower end of spin beam 2 and are aligned and in fluid communication with horizontal channel section 8. Thus, the molten polymer stream traveling into horizontal channel section 8 of the “coat hanger” channel proceeds to flow through screen filter and support plate 9 to spinneret 10, where the polymer stream is then extruded through the spinneret orifices to form a plurality of polymer filaments. The “coat hanger” channel configuration is particularly advantageous because it is simple in design and creates a substantially uniform pressure differential within the channels, resulting in a uniform delivery of the polymer stream into the horizontal channel portion of the “coat hanger” channel and uniform extrusion of molten polymer through the spinneret orifices.
While a closed fiber spinning system combined with a “coat hanger” spin beam is useful for manufacturing certain polymer fibers having desirable uniformities and deniers, the “coat hanger” spin beam encounters problems when two or more different polymer components are utilized to produce more complex fibers and spunbond webs of fibers. In particular, it is very difficult in a “coat hanger” closed system to process two or more different polymer components having different melting temperatures when manufacturing multicomponent fibers or fabrics containing multiple polymer components. For example, a bicomponent fiber consisting of two polymer components with significantly different melting points would be extremely difficult to produce utilizing a closed spinning system with a “coat hanger” spin beam (e.g., by utilizing a double “coat hanger” spin beam with “coat hanger” channels being arranged in a side-by-side manner), because the “coat hanger” spin beam would tend to be maintained at substantially the same temperature by the electrical heaters disposed in the spin beam sections. The difficulty is further exacerbated when utilizing polymer components that must be maintained at or very near their melting temperatures to avoid gelling or cross-linking of the polymers. Moreover, while the “coat hanger” systems deliver a uniform molten polymer stream to the spinneret, it is difficult to modify the metering of the molten polymer stream through the “coat hanger” spin beam to the spin pack, which is an important feature in manufacturing more complex types of fibers such as multicomponent fibers having varying geometries and/or polymer component cross-sections. Thus, the flexibility of “coat hanger” spin beams is very limited in enabling the manufacture of a wide variety of different fibers and fabrics within a closed fiber spinning system.
Accordingly, there exists a need for producing a wide variety of fibers and fabrics including two or more polymer components in a closed fiber spinning system and with a spin beam capable of delivering molten polymer streams of two or more different polymer components for fiber production within the closed system.